An analog-to-digital converter (ADC) is employed to change/convert an analog input signal into a digital output signal. There are several different types of ADCs in current use, including pipeline, flash and folding. For pipeline ADCs, separate decoding stages are arranged in a pipeline to convert the analog signal into a digital signal.
In a flash ADC, k bits of resolution employ 2k comparators to convert an analog signal into a digital signal. Folding ADCs are a variation of a typical flash ADC architecture except that they are arranged to map the analog input signal range into N regions where each of these N regions share the same comparators. In a folding ADC, the total number of comparators is typically 2k/N. Also, a folding ADC includes a coarse channel for determining from which of the N input regions the analog input signal originated. Usually, the coarse channel is configured to use coarse reference voltages that are spaced according to the voltage spacing between each folding region.